Call out people who do. Tell them it's not okay.

Especially with other people around. Many people know it's not right, but don't want to say anything because they're afraid of confrontation. But if someone says it's not cool, they'll be more likely to say something backing you up.

There's some great advice available online. I tried looking up some examples but it's hard to pick one site. So if you're looking, you can start here